1. Field of the Invention
The present invention relates to the fabrication of integrated circuits. More particularly, the invention provides a cleaning technique for a plasma chamber utilized in the manufacture of integrated circuits.
2. Background of the Invention
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition or CVD. Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film. The high temperatures at which some thermal CVD processes operate can damage device structures having metal layers previously formed thereon.
Processes which have been developed to deposit insulation films over metal layers at relatively low temperatures include plasma-enhanced CVD (PECVD) techniques such as described in U.S. Pat. No. 5,362,526. Plasma-enhanced CVD techniques promote excitation and/or disassociation of the reactant gases by the application of radio frequency (RF) energy to a reaction zone near the substrate surface, thereby creating a plasma of highly reactive species. The high reactivity of the released species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperature for such PECVD processes. A known PECVD process is the plasma enhanced reaction of tetraethylorthosilicate (TEOS) and oxygen (O2).
The surface upon which a CVD layer is deposited may contain sorbable contaminants such as fluorine deposits from chamber cleaning or other processes. The presence of fluorine or other sorbable contaminants may affect the absorption of precursors and slow or inhibit the deposition rate of the CVD layer. Fluorine in the chamber can also form particles when contacted by the reactive gases used to make a PECVD oxide layer.
Particle contamination within the chamber is typically controlled by periodically cleaning the chamber using cleaning gases, typically fluorinated compounds, that are excited to inductively or capacitively coupled plasmas. Cleaning gases are selected based on their ability to bind the precursor gases and the deposition material which has formed on the chamber components in order to form stable volatile products which can be exhausted from the chamber, thereby cleaning the process environment.
Once the chamber has been sufficiently cleaned of the process gases and the cleaning by-products have been exhausted out of the chamber, a season step is performed to deposit a film onto components of the chamber forming the processing region to seal remaining contaminants therein and reduce the contamination level during processing. This step is typically carried out by depositing a season film to coat the interior surfaces forming the processing region in accordance with the subsequent deposition process recipe.
While chamber cleaning and depositing a season film have been successful in reducing most contaminants in a plasma reactor, sorbable contaminants such as fluorine have still been measured above desired levels. Therefore, there exists a need for a method for further reducing sorbable contaminants within a plasma reactor. It is an object of this invention to provide such a method and an integrated apparatus for performing the method.
The present invention provides a method and apparatus for reducing fluorine and other sorbable contaminants in a plasma reactor used in a chemical vapor deposition process. According to a method of the present invention, a plasma of an inert gas is maintained in a plasma reactor following a chamber clean to remove sorbable contaminants such as fluorine. The plasma clean is typically followed by seasoning of the reactor components with a film to block or retard remaining contaminants. According to one embodiment of the invention, the combination of a chamber clean, a plasma clean, and a season film is conducted before a wafer is positioned in the plasma reactor and a PECVD oxide layer is deposited on the wafer. The plasma reactor is controlled by a computer which is programmed for selection of the chamber clean, the plasma clean, and the season film.